Interlocked Mode - National Instruments MXI Series Getting Started

Interlocked Mode

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VXI/VME-MXI-2 itself via its requested memory space from both the
VXI/VMEbus and the MXIbus. For more information on the A16, A24, and
A32 windows, refer to VXI-6, the VXIbus Mainframe Extender
Specification.
Interlocked arbitration mode is an optional mode of operation in which at
any given moment the system can perform as if it were one large
VXI/VMEbus mainframe with only one master of the entire
system—VXI/VMEbus and MXIbus. This mode of operation prevents
deadlocks by interlocking all arbitration in the VXI/VMEbus/MXIbus
system. By default, this option is disabled, which puts the
VXI/VME-MXI-2 in normal operating mode.
In normal operating mode (non-interlocked), multiple masters can operate
simultaneously in the VXI/VMEbus/MXIbus system. A deadlock occurs
when a MXIbus master requests use of a VXI/VMEbus resource in another
VXI/VMEbus mainframe while a VXI/VMEbus master in that mainframe
is in the process of requesting a resource across the MXIbus. When this
situation occurs, the VXI/VMEbus master must give up its bus ownership
to resolve the conflict. The RETRY signal is used to terminate the transfer
on the VMEbus; however, devices in the VXI/VMEbus mainframe must be
able to detect a RETRY caused by a deadlock condition so that they can
retry the operation. Any master device that cannot detect the retry protocol
will interpret the response as a BERR signal instead.
The VXI/VME-MXI-2 is shipped from the factory configured for normal
operating mode (non-interlocked). If MXIbus transfers will be occurring
both into and out of the mainframe and the VXI/VMEbus modules in your
system do not have the capability for handling retry conditions, you may
want to configure the VXI/VME-MXI-2 for interlocked arbitration mode
by clicking on the Enable checkbox. In this mode, no software provisions
for deadlock conditions are required. However, parallel accesses in separate
VXI/VMEbus mainframes are no longer possible, and system performance
may be lower than in normal operating mode.
In a VXI/VMEbus/MXIbus system, you can configure some
VXI/VME-MXI-2 modules for normal operating mode and others for
interlocked arbitration mode. The VXI/VMEbus mainframes configured in
interlocked arbitration mode will be interlocked with each other and the
mainframes configured for normal operating mode can perform transfers in
parallel.
Chapter 6
6-21
NI-VXI Configuration Utility
PCI-MXI-2 for Linux